6 ms·
I expected that 1kW would be a drop in the bucket for a car, since moving that huge hunk of metal from A to B seems like it should totally dominate. But I worke
by imh 10y ago
I expected that 1kW would be a drop in the bucket for a car, since moving that huge hunk of metal from A to B seems like it should totally dominate. But I worked it from first principles, and sanity checked against Tesla anecdotes [0]. At usual speeds and 2.5-3 mi/kWh [0], that's a power consumption in the tens of kW [1], so call 1kW a 5% bump. According to CNN[2], that could be around ~$20/mo from super rough back-of-the-envelope math.
If that estimate is on the money or high, I'd totally pay <= $20/mo for my car to drive itself. If it's low, I probably wouldn't pay $100+/mo for it.
[0] https://forums.tesla.com/forum/forums/miles-kwh https://forums.tesla.com/forum/forums/miles-kwh
[1] X mph / (Y mi / kWh) = X/Y kW
[2] http://money.cnn.com/2011/05/05/news/economy/gas_prices_income_spending/index.htm http://money.cnn.com/2011/05/05/news/economy/gas_prices_inco...
- foota 10y agoYou might be willing to pay $20/mo, but how much do you think Tesla would be willing to pay to increase their range by 5%?
- imh 10y agoI wrote out the numbers I worked out for a tesla, but I had also done it from basic physics (plus referenced efficiencies) for a gas car, and it's not horribly different. I didn't include it because I have no idea what so ever how big of a deal adding in a 1kW power system to a gas car that still drew power from the gas engine, or what the losses look like. The order of magnitude remains about the same. I drive a prius, and if my estimate is close enough, the range isn't a factor for cars like mine. I was mostly curious in order of magnitude kW stuff, and only tangentially $ stuff.
- deevolution 10y agoAlso consider whatever you value your hourly rate. You can work/do whatever you want for an extra hour in a driverless car on your way to work but you cant do that in a traditional car. There are other cost factors here besides electricity/gas.
- llukas 10y agoSo you put extra 1kW heater somewhere in the car. Now how much energy you spend on cooling?
- ak217 10y agoInternal combustion engines are 20-45% efficient. That means a 150 hp car dissipates 55 KW at peak. Assuming half load that's over 25 KW to dissipate continuously. Cars usually dissipate heat by way of a ~100 kg radiator, ram air and a couple of 20W fans. Brakes dissipate far larger amounts of heat in short bursts, and are passively cooled by ram air. For EVs, I'm not sure, but I think 100KW li-ion pack will continuously emit something between 1-5KW in heat when charging or discharging. 1KW is a small fraction of a typical car's heat budget.
- Baeocystin 10y agoI agree with your general point, but to sanity check your numbers: car radiators don't even weigh a tenth of that. The entire cooling system, including fluid, is in the sub-20kg range. The entire drivetrain of a common 4-banger is in the 150-160 kilo range.
- hinkley 10y agoExcept it only takes about 20hp to keep a car at highway speed. The rest is for acceleration, hills, headwinds and looking cool.
- mborch 10y agoThe brain can drive a car and uses a fraction of that amount of energy.